Numerical Study On Risk Of Storm Surge Induced By Cold-air Outbreak In The Bohai Sea

Storm surge can be ranked as the most serious disaster among the marine disasters.Most of the serious disasters that occurred along the coastal zone are associated with storm surges induced by extreme weather systems.In China, almost all the coastal zones are susceptible to storm surges. In the coastal zone of the south-east part of China, storm surges are usually induced by typhoons or tropical cyclones that generate over the northwestern Pacific, but in the Bohai Sea, which is located in the high latitude and seldom affected by typhoons and tropical cyclones, storm surges caused by cold-air outbreaks in winter usually lead to a sustained significant sea level rising along the south-western coastal zone.By analyzing the characteristics of cold-air outbreaks, three typical characteristics are summarized to calculate the storm surge.After the sensitivity experiment with these characteristics, the cold-air outbreaks are divided into four categories according to the major track by which they attack China, and in each category there are one control scenario and four more extended scenarios. Therefore,the cold-air outbreaks over the Bohai Sea are described by these 20 scenarios.Base on these cold-air scenarios, storm surges induced by cold-air outbreaks in the Bohai Sea are modeled by FVCOM.It is find that the tops of the Bohai Bay and the Laizhou Bay are most seriously affected by the storm surges in the Bohai Sea.The characteristics of storm surges change with the tracks of cold-air outbreaks.The cold-air outbreaks from the NW and N track could place both the Bohai Bay and the Laizhou Bay at risk, the cold-air outbreaks from NE track usually lead significant water level rising to the top of Bohai Bay, but the ones from W track can only affect the Laizhou Bay. After the discussion of the water level rising induced by cold-air outbreaks, the risk of storm surge in Tanggu, Huanghua and Yangjiaogou is analyzed.As the most concerned areas, the risk of inundation in Tanggu and the Yellow River Delta is investigated respectively according to the strength of the cold-air outbreaks. In order to estimate the risk along the coast more reasonably, the time period that the water level exceeds a given threshold is involved.Based on the function considering the surge elevation, the probability of the storm surge scenarios and the time period mentioned above, the risk along the coast of the Bohai Sea is estimated, and the distribution of risk of storm surge along the Bohai Sea can be presented easily and clearly by this method.Strom surges are not only determined by the atmospheric forcing, but also influenced by many other factors, such as the coastal geometry and bathymetry, sea level rising caused by climate change and underground water. As the coastline of the Bohai Sea has changed evidently in the Caofeidian area and Yellow River Delta these years, storm surges in the Bohai Sea may have some new characteristics due to the local changing of the geometry. To find out these new characteristics, the influence of the changes in coastal geometry on storm surges is primarily investigated by numerical methods by involving the coastline of the Bohai Sea during 1976,2010 and 2030.By comparing the amplitude of astronomic tide, the distribution of maximum surge elevation and the risk of the storm surge during different periods, the main changes made by the variation of the coastline in Caofeidian and the Yellow River Delta can be found in the Bohai Bay and the Laizhou Bay. In the Bohai Bay, the amplitude of astronomic tide, the distribution of maximum surge elevation and the risk of the storm surge are all found decreasing with the changing of coastline, however, in the Laizhou Bay, all these terms are enhanced by the changing Yellow River Delta.